A number of important aspects of normal hearing are known to be dependent upon the presence of duplicate sets of functioning ears. Persons who have lost the use of one ear frequently find themselves at a distinct disadvantage in a variety of everyday situations ranging from locating the sources of unexpected sounds to carrying on intelligent conversations at noisy cocktail parties. The neural mechanisms involved in these binaural hearing functions are, at present, poorly understood. Using the cat as the experimental subject, the objectives of the present proposed research are (a) to investigate the respective contributions made by the neocortical and thalamic divisions of the auditory nervous system to a number of different binaural hearing phenomena; and (b) to investigate the functional significance of bilateral paired structures at the thalamic and cortical levels. The ultimate goal of this research is to provide a fuller understanding of the neurological mechanisms involved in normal binaural listening in both cat and man. Both monaural discrimination and binaural integrative tests will be used in the proposed series of experiments. BIBLIOGRAPHIC REFERENCES: Cranford, J.L. Auditory masking-level differences in the cat. J. Compl Physiol. Psychol., 89 (1975) 219-223. (Reprints enclosed). Cranford, J.L. Role of neocortex in binaural hearing in the cat. I. Contralateral masking. Brain Research, 100 (1975) 395-406.